Bio-sand water filtration removes bacteria from water using both physical and biological methods. It is a large container, (plastic barrel or cement tank) containing layers of pebbles, grit and fine sand. Water poured into the top of the unit slowly percolates through the sand and grit to a pipe in the bottom of the container. Hydrostatic pressure, pushes the water up to the outlet tap from where it can be collected.
With use over a period of several weeks, micro organism from the source water collect on the upper layer of fine sand to develop a biological layer, the Schmutzdecke. This layer assists in the removal of pathogens by biological processes as the microorganisms build up a thriving ecosystem and feed on bacteria and other pathogens in the source water. Design of the bio sand filtration unit ensures that a layer of standing water is maintained above the schmutzdecke at all times to aid survival of this biological layer and enhance biological filtration.
The units are easy to maintain as they are simple in design and require no expertise to clean and repair. Research indicates that the units will last for up to ten years before the sand needs to be replenished. Over time the flow rate of water through the system may be reduced as the schmutzdecke layer develops and air spaces in the sand medium become clogged. This is simply fixed by stirring up this fine layer then scooping the dirty water from the top of the unit. A new schmutzdecke layer quickly begins to form. This cleansing process can be carried out as often as needed.